Holography is a method by which the wave field of light is recorded as an interference pattern, sometimes called a lensless system since the usual lens required in optics is replaced by a film having zone plates that diffract and thereby focus the light. The process of interference is involved wherein wave length and phase establish "constructive interference" that increases amplitude, and "destructive interference" that decreases amplitude. The interference effect normally requires that the light be coherent; coherent light being monochromatic (having a single wave length) that maintains the form of its phase fronts. That is, successive wave fronts, as they pass a given location, all have the same shape. Therefore, laser light is a most appropriate source of coherent light, to be used in producing holograms for the purpose herein disclosed. The technique of "off-axis holography", produced with a reference beam of light introduced obliquely with respect to the subject beam of light, enables the straight-through or unaffected light to be separated, since the various waves travel in different directions.
The significant holographic feature employed herein is the "volume hologram" in which the thickness of the film or recording medium accommodates a multiplicity of "zone plates" in the form of interference patterns embedded within the thickness of the film or recording medium and each passing a descrete frequency of light. Diffraction from volume holograms is orientation sensitive, whereby many sets of wave patterns can be recorded in a single volume hologram, each with the recording material having a slightly different orientation. When the hologram is subject to the passage of light, only one set of waves at a time can have the proper orientation to produce a diffracted wave. When the light source is rotated slightly with respect to the plane of the film, the one diffracted wave is extinguished and another diffracted wave appears. Thus, the hologram exhibits wavelength selectivity. For light incident on the hologram at a given angle, the diffracted light is formed only for the light of proper wavelength, the wave length selectivity being greatest when the subject and reference beams are introduced from opposite sides of the film, this type of hologram being known as the "white light hologram" because it diffracts white light from a source. This type of hologram selects only a narrow band of light out of the wide band of wave lengths that comprise white light, this narrow band of light being diffracted by the hologram. The remaining light passes through the hologram without diffraction. The volume recording medium can be a photographic emulsion of moderately great thickness, or a number of layers of light sensitive material that can be darkened by exposure to coherent light, for recording to establish interference patterns.
Diffraction is an important phenomenon in holography, a grating employed at the zone plates whereby light is deflected, and herein to have a variable lens function. Accordingly, different gratings of zone plates are established by laser photography or the like, whereby permanent holograms are established in one or more zone plates as multiple slit gratings. In the photographic recording of holograms, the change from transparent to opaque areas is gradual rather than sudden, and this causes the light amplitude to vary gradually. This sinuous variation in light amplitude has its advantageous effect in diffraction analogous to refraction in a solid transparent lens or the like. In holography, the light passes around opaque objects (diffraction) rather than through a substance (refraction), but nevertheless the direction of certain light waves is altered. In holography, the interference pattern generated by sets of light waves is three dimensional in extent, and when such a pattern is recorded as by photography, it does not merely exist at the surface of an emulsion or film, but establishes itself in plates throughout the volume or thickness of said emulsion or film. Therefore, photographically produced gratings or zone plates of holograms are considered as recorded wave interference patterns through which multi-color light behaves according to wavelength. A zone plate can be described as a set of flat, parallel lines or concentric annular rings which diffract light waves so that they are columnated or so that add constructively at a desired focal point, preventing the passage of light waves that would interfere destructively at that point. The emulsion of a photographic plate or film may be many, perhaps twenty, or more, light wavelengths in thickness, so that three dimensional patterns can be established as distinctively effective zone plates.
It is an object of this invention to achieve the insolation of solar energy through the use of a fixed diffraction panel or panels in combination with a reflector dish which serves as a microwave receiver or transmitter. Heretofore, simple solar panels have been fixed to face skyward toward the suns traverse, and more sophisticated concentrators have been focused at the sun throughout its traverse by means of tracking devices. The efficiency of the fixed solar panels is wanting, while the complexity of tracking systems involves considerable expense in the initial construction and in the continued operation thereof. Therefore, a fixed installation devoid of tracking mechanisms is to be desired, this being the primary object of this invention.
This invention is characterized by fixedly positioned collector and concentrator holograms that have diffraction capability inherent in a holographic window to direct sunlight along the collector axis. Holography involves interference patterns between two or more sets of light waves, and by which films or laminates are formed with certain gratings that will selectively function as lenses that focus certain wavelengths of light. Accordingly, films with distinctive gratings will have varied and predetermined focusing characteristics, established photographically as zone plates and each adapted to redirect and focus light waves of a certain wavelength. The angle of redirection or diffraction can be great, so that sunlight at a low angle of incidence can be redirected as light moves through the hologram grating which then focuses those waves by means of diffraction, similar to lens refraction, to emanate substantially normal therefrom or within a prescribed angle thereto. In practice, a multiplicity of hologram zone plates are established in layers and together establish distinctive grating zones acting together to focus sunlight with diminishing effect from a low angle of incidence to a high angle of incidence or to the Zenith, and so that light wave transmission through the holographic laminate emanates substantially normal therefrom at all times of day between shortly after sunrise and shortly before sunset. This primary diffraction of the incoming sunlight will be referred to herein as "normalizing" the light, a redirecting of incoming white light into selected wavelength light projected in an alignment substantially parallel to the axis of the collector. The holograms are preferably planar as shown herein, as distinguished from the reflector dish for micro wave transmission.
All sunlight is received as white light that passes selectively through holographic laminates or plates, the infrared (IR) wave portion of the spectrum being separated for heat absorption, and the ultraviolet (UV) portion of the spectrum being separated for photo voltaic power generation. It is an object of this invention to receive white solar light and to separate it into distinct wavelength ranges while normalizing its projection to occur parallel with the axis of the collector. In accordance with this invention, spectrally selective holograms comprised of circularly concentric gratings are provided to separate the infrared portion of the spectrum from the ultraviolet portion of the spectrum while normalizing the same along the collector axis. In practice, the infrared portion is concentrated and the ultraviolet portion is columnated, there being hologram gratings for infrared light diffraction and a hologram gratings for ultraviolet light diffraction. The range of wavelength diffraction can be established within practical limits as circumstances require.
It is another object of this invention to project the normalized incoming light separately as infrared and ultraviolet light into a heat absorption receiver of a power generator and onto a photo voltaic power generator, respectively. Accordingly, there is a first spectrally focusing hologram comprised of circular gratings having a focal plane for concentrating infrared heat rays, and there is a second columnating hologram that projects said ultraviolet light onto a photo voltaic power generator plane at or surrounding the said concentration of infrared light. A feature of this invention is that the infrared light diffracted by an overlying hologram unaffectedly passes through an underlying hologram that separately diffracts ultraviolet light, or vice versa, the one light passing unaffectedly through the overlying hologram to be diffracted by the underlying hologram. Diffracted light in both instances is normalized and projected along or parallel to the collector axis. It is an object of this invention to advantageously employ a Rankine cycle power generator, a gas turbine or the like, at said focal plane of infrared light, and to advantageously employ photo voltaic cells at said plane thereof surrounding said power generator. It is also an object of this invention to superimpose photo voltaic cells upon a substrate in the form of a micro wave reflector, the holograms and photo voltaic cells having little or no adverse effect upon micro wave reception.
It is still another object of this invention to combine a solar collector (UV) and concentrator (IR) with a micro wave dish that simultaneously serves in the capacity of a satelite receiver and Rankine cycle condenser. A feature of this invention is that micro waves penetrate the hologram plates without being adversely affected, and also penetrates the lattice of the photo voltaic cells. As shown, the substrate and structural support for the micro wave dish is finned for heat radiation from a condenser coil of the Rankine system. The micro wave dish focuses at a feed assembly removed from the concentration of infrared light.
It is a general object of this invention to provide for co-generation of electricity whereby Rankine cycle power and photo voltaic power are combined and synchronized with an alternating power source that is external. In practice, the Rankine cycle power generator is of the induction type with the photo voltaic power generation commutated therewith as synchronized alternating current, the combination of the two being synchronous with the external alternating electrical power source by virtue of the induction type generator used herein.